Accumulated Other Comprehensive Income (Loss) (Schedule of AOCI) (Details) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance				$ (105,172)
Ending balance		$ (102,930)		(102,930)
Foreign Currency Translation
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(11,850)	$ (26,420)	(16,183)	$ (27,828)
Cumulative-effect adjustment for the adoption of ASU 2017-12						$ 0
Amounts recognized into AOCI		(7,392)	5,589	(3,059)	6,997
Currency impact		0	0	0	0
Amounts reclassified from AOCI, Currency		0	0	0	0
Tax effect		0	0	0	0
Other comprehensive income (loss), net of tax		(7,392)	5,589	(3,059)	6,997
Ending balance		(19,242)	(20,831)	(19,242)	(20,831)
Derivative Instruments
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		1,546	(350)	351	(515)
Cumulative-effect adjustment for the adoption of ASU 2017-12						(275)
Amounts recognized into AOCI		603	(858)	2,067	(1,124)
Currency impact		0	0	0	0
Amounts reclassified from AOCI, Derivatives	[1]	(4)	382	337	900
Tax effect		(127)	(87)	(462)	(174)
Other comprehensive income (loss), net of tax		472	(563)	1,942	(398)
Ending balance		2,018	(913)	2,018	(913)
Pension and Other Post-retirement Benefits
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(88,585)	(96,398)	(89,340)	(96,854)
Cumulative-effect adjustment for the adoption of ASU 2017-12						0
Amounts recognized into AOCI		1,527	4,801	1,527	4,801
Currency impact		524	(258)	40	(738)
Amounts reclassified from AOCI, Pension/PRW	[2]	1,564	1,206	3,170	2,670
Tax effect		(736)	(2,755)	(1,103)	(3,283)
Other comprehensive income (loss), net of tax		2,879	2,994	3,634	3,450
Ending balance		(85,706)	(93,404)	(85,706)	(93,404)
Accumulated Other Comprehensive Loss
Change in Accumulated Other Comprehensive Loss [Roll Forward]
Beginning balance		(98,889)	(123,168)	(105,172)	(125,197)
Cumulative-effect adjustment for the adoption of ASU 2017-12						$ (275)
Amounts recognized into AOCI		(5,262)	9,532	535	10,674
Currency impact		524	(258)	40	(738)
Amounts reclassified from AOCI		1,560	1,588	3,507	3,570
Tax effect		(863)	(2,842)	(1,565)	(3,457)
Other comprehensive income (loss), net of tax		(4,041)	8,020	2,517	10,049
Ending balance		$ (102,930)	$ (115,148)	$ (102,930)	$ (115,148)

[1] We reclassified natural gas contracts through cost of sales and the interest rate swap through interest expense on the Condensed Consolidated Statements of Operations. See note 8 for additional information.

[2] We reclassified the net pension and non-pension post-retirement benefits amortization and settlement charges through other income (expense) on the Condensed Consolidated Statements of Operations. See note 6 for additional information.